The present invention is directed toward a method for liquefying target tissue within a body and more particularly, toward a method of heating a biocompatible fluid and presenting such to target tissue, thereby liquefying the target tissue and aspirating it while leaving non-target tissue intact.
Prior thermal energy sources used in surgery have been “dry-heat” devices. Some examples are: thermal lasers, ultrasound, microwave, radio frequency, and electrosurgery devices. These dry-heat energy sources transfer heat from a surgical instrument to a tissue primarily by the heat transfer modalities of conduction and radiation. Thermal lasers, ultrasound, and microwave energy sources can liquefy tissue, but only at very high energy levels. If any of these dry-heat energy sources are placed in direct contact with target surgical tissue, there is no tissue differentiation. That is, healthy as well as unhealthy tissue will be liquefied. For example, collapsing cavitation bubbles in front of an ultrasound surgical instrument release a thermal energy of 13,000° F. per bubble. With such a high thermal energy input there is no differentiation of tissue within the surgical tissue field. That is, all tissue target and non-target, within the target field melts or liquefies. The thermal energy in thermal lasers and ultrasound is inherently high, so the heat cannot be “turned down” or reduced. In microwave, radio frequency, and electrosurgery the level of thermal energy may be reduced but in so doing, liquefaction of tissue is not achieved at all. Rather, cauterization or coagulation of the tissue results.
U.S. Pat. No. 4,924,863 discloses a method for removing artherosclerotic plaque from a patient by heating the plaque under pressure for a limited period of time. When the plaque is heated, it liquefies without causing immediate death of the underlying tissue. The liquefied plaque is then aspirated from the body through a catheter. The means used for heating the plaque is microwave or radio frequency energy. As discussed above, however, in an effort to control the level of energy being produced, all of the plaque may not liquefy.
U.S. Pat. No. 5,540,679 discloses the use of a balloon catheter for heating tissue in a patient's body. A heating device is located within the balloon and is arranged for heating fluid inside the balloon. When the fluid is heated, unwanted tissue, such as a tumor or an enlarged prostate gland, is heated by thermal conduction from the fluid through a wall of the balloon. The heat destroys the tissue which is eventually absorbed into the patient's body. This method uses conduction and as explained above, such a method creates such a high level of energy that there is no tissue differentiation. As a result, healthy tissue may be heated and ultimately destroyed.
U.S. Pat. No. 4,886,491 discloses a method of liposuction using an ultrasonic probe. An ultrasonic probe tip is vibrated at a high frequency and a low amplitude. This method separates the fatty tissue and creates heat which melts some of the fatty tissue. A saline irrigating solution is applied to the area which emulsifies the melted fatty tissue. The emulsified solution is then aspirated. Again, because of the high thermal energy input into the system there is no differentiation of tissue into target and non-target tissue.